JP-4449942 B2 teaches an electronic control device having a battery, a motor generator as a vehicle driving power source, a three phase inverter arranged between the battery and the motor generator and executing electricity conversion between the battery and the motor generator, and an electric continuously variable transmission. The electronic control device is mounted on the vehicle. The motor generator is defined as a MG, and the electric continuously variable transmission is defined as an electric CVT.
In the electronic control device, when an upper arm or a lower arm in one of phases in the three phase inverter short-circuits, and the rotation speed of the MG is higher than a predetermined rotation speed, all of the upper arms or all of the lower arms in three phases are controlled to turn on at the same time. Thus, when the three phase on-control is performed, the regeneration torque (i.e., brake torque) generated by the MG becomes smaller than a case where one phase short-circuits.
Recently, in order to drive the vehicle similar to the manual transmission, many vehicles use an electric CVT that is capable of shifting a transmission by an operation of a driver of the vehicle. The electric CVT is also defined as a CVT having a sequential shift function.
When the driver operates the shift lever to shift down the transmission, it is necessary for the vehicle to generate a negative torque corresponding to the shift down operation and to reduce a vehicle speed. For example, in the vehicle having the electric CVT, when it is necessary for the MG as the driving power source to generate the negative torque, the negative torque is to be generated at the MG in a manner without generating regeneration current if it is impossible to charge the battery.
On the other hand, it is considered that the negative torque may be generated at the MG using a technique for performing a three-phase on control. However, in this technique, since all of the upper arms or all of the lower arms in the three phases turn on at the same time, and the on-state of the three phases continues, it is difficult to generate the negative torque corresponding to the shift down operation. Specifically, it is difficult to adjust or control the negative torque generated at the MG to be a required negative torque.